Actually, the view of behavioral geneticists, including those with whom I have a weekly discussion of current research,

http://www.psych.umn.edu/courses/fall09/mcguem/psy8935/defau...

is that each individual has a "reaction surface," a range of possible behavioral responses genetically endowed for that individual depending on what environmental influences that individual encounters. NO ONE active in the field of behavorial genetics claims to have proved that many individuals today have maxed out their potential for intelligent behavior. There may be (as yet unknown) interventions that could massively change IQ at the individual level.